Method of applying helical fins to tubes



Oct. 10

E. BRUEGGER 2,525m92 METHOD OF APPLYING HELICAL FINS TO TUBES Filed Oct.30, 1948 Fig]- ig.3;

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INVE R I BY I j m I Patented Oct. 10, 1950 METHOD OF APPLYING HELICALFINS TUBE Ernest Bruegger, Massillon, Ohio, assignor to The GriscomRussell Company, New York, N. Y., a corporation of Delaware ApplicationOctober 30,1948, Serial No. 57,527

3 Claims. I This invention relates to finned tubing and the method ofmaking the same, and more particularly to an improvement upon the typeof finned tubing shown, for example, in the patent to Berg, No.1,668,534. Tubing of the type shown inthis patent is widel used in manyforms of heat exchangers, particularly the so-called atmospheric coolerswherein the liquid to be cooled is circulated in the tubes and air iscirculated over the finned outer surface of the tubes. In suchtubes itis important that the joint between the base of the fin and the tubewall be a good heat conducting joint. Otherwise the eificiency of thefin surface is greatly impaired.

As the thickness of the tube wall from the base of the grooves to theinside of the tube must be suflicient to withstand the internal pressureto which the tube is subjected, a deep groove can be obtained only atthe expense of adding metal to the tube beyond the amount required forthe pressure of the liquid to be handled. It is therefore desirable tolimit the depth of the grooves of the tube wall as far as possibleconsistent with having a mechanically tight and good heat-conductingjoint between the base of the fin and the tube wall.

The object of my invention is to increase the mechanical strength andthe heat conductivity of the joint between the base of a helically woundfin and the tube upon which it i wound without necessitating an increasein the depth of the grooves, as would be required in the manufacture oftubing such as disclosed in the above mentioned Berg patent. I attainthis result primarily by cutting the grooves in the tube at an angle tothe tube surface so that the depth of the groove from the standpoint ofthe width of the fin edge which is in contact with the metal of thegroove is substantially increased without reducing the thickness of thetube wall from the base of the groove to the interior surface of thetube. The inner edge of the helically wound fin is also bent at an angleto the plane of the portion of the fin which will be exposed after thefin is applied to the tube, and the metal of the tube adjacent thegroove is compressed down over the bent foot of the tube so that thearea of the metalto-metal contact around the base of the tube issubstantially double that obtained in a tube of conventionalconstruction such as shown in the above mentioned Berg patent.

In the accompanying drawings I have illustrated two somewhat differentmodifications of my improved tubing and, referring to the drawings,

Fig. 1 is an enlarged sectional view of a portion of a tube after it isgrooved in accordance with my improvement and with the base of the fininserted in the groove;

Fig. 2 is a similar section of the finished tube showing the effect ofthe crimping roller on the metal forming the joint between the fin andthe tube;

Figs. 3 and 4 are views similar to Figs. 1 and 2, respectively, showinga somewhat modifie form of groove; and

Fig. 5 is an elevational view on a smaller scale of a short section oftubing embodying my invention.

Referring to the drawings, particularly Figs. 1 and 2, I indicates thetube wall and 2 the fin. the thickness of the metal being considerablyexaggerated. The fin 2 as shown in'Fig. 5, is helically wound around thetube to provide closely spaced fins, as there illustrated. The base 3 ofthe fin, that is, the inner edge of the fin as it is wound around thetube, is turned at an angle to the plane of the fin of about 60 and thetube is formed with a helical groove of triangular cross section, asshown at 4 in Fig. 1, with the plane of the base of the groove at anangle of 60 to the surface of the tube.

The groove is preferably formed by a cuttin instrument which is shapedto turn the metal taken from the groove outwardly at substantially rightangles to the outer surface of the tube, forming a helical rib 5 asshown in Fig. 1, and is preferably undercut as shown. After the fin iswound around the tube, which may be accomplished in any approved manner,the metal of the projecting rib 5 is pressed down against the base ofthe fin in the manner shown in Fig. 2 by a pressing roller having itsperimeter of suitable contour to properly shape the metal over the baseof the tube and at the same time compress the flange at the base of thetube outwardly at its edge to snugly fit within the un dercut portion ofthe groove. After the pressing operation is complete the fin is firmlyanchored in the metal of the tube and the area of the metal-to-metalcontact at the base of the fin is over twice as great as could besecured according to the method of the Berg patent above cited with asimilar tube without further reducing the wall thicknes between the baseof the groove and the interior surface of the tube.

In Figs. 3 and 4 I have shown a somewhat modified form of my invention,and as here shown, the groove in the tube is not undercut as in thepreferred construction shown in Fig. I. That is to say, the face of therib la is at a somewhat obtuse angle to the axis of the tube so that theedge or the fin which is at right angles to the face of the finsubstantially fits the groove as it is wound upon the tube.

The metal of the rib 5a is rolled down and compressed against the baseof the fln in the manner previously described, but as the base of thefin fills the groove there is no compression of the base metal into anundercut portion of the groove.

My improved tube may be made in various ways. either by winding the fiatmetal stri p directly upon the grooved tube, thereby coiling the fin andbending the inner edge to the appropriate angle at one operation or, ifdesired, the fin may be formed and precoiled before it is applied to thetube. Both methods are in wide use in the manufacture of finned tubingof the type shown in the above mentioned Berg patent. It will also ofcourse be understood that the inner edge of the fin may be bent to agreater or less angle to the plane of the fin than here shown and mayalso be curved, if desired, or otherwise shaped to present a portion ata substantial angle to the main radial portion of the fin to therebyincrease the area of the metal-to-metal joint between the fin and thetubing without increasing the depth of the groove in the tube wall.

It will also be understood that my invention is otherwise not limited tothe precise structure shown and described herein, but may be variouslymodified within the scope of the appended claims.

I claim:

1. The method of making heat exchanger tubes which comprises forming inthe tube wall a helical groove having its base at an angle to the wallof the tube. and simultaneously turning the metal from the grooveoutwardly to form a ridge 4 of metal at the deeper edge of the groove,winding a fin in the groove with the side of the fin at its base portionfiat against the bottom of said groove, and then pressing the ridge ofmetal over and against the outer side of the base of the fin.

2. The method of making heat exchanger tubes which comprises forming inthe tube wall a helical groove having its base at an angle of about 30to the wall of the tube, and simultaneously turning the metal from thegroove outwardly to form a helical ridge of triangular cross-section,winding a fin in the groove with the side of the fin at its base portionfiat against the bottom of said groove, and then pressing the ridge ofmetal over and against the outer side of the base of the fin.

3. The method of making heat exchanger tubes which comprises forming inthe tube wall a helical groove having its base at an angle of about 30to the wall of the tube, and simultaneously turning the metal from thegroove outwardly to form a helical ridge of triangular crosssection,bending a metal ribbon along one edge to an angle to the main width ofthe ribbon to form a fin having a base portion, winding the fin in thegroove with the side of the fin at its base portion fiat against thebottom of said groove, and then pressing the ridge of metal over andagainst the outer side of the base of the fin.

ERNEST BRUEGGER.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 808,490 Swan Dec. 26, 1905851,977 Bigsby Apr. 30, 1907 1,928,639 Berg Oct. 3, 1933

